1. Field of the Invention
The present invention relates to a refrigeration cycle apparatus comprising two compressors used for a plurality of indoor heat exchangers and a outdoor heat exchanger.
2. Discussion of Backgrounds
FIG. 6 shows construction of a conventional refrigeration cycle apparatus. In FIG. 6, reference numerals 1 and 2 designate first and second compressors, a numeral 3 designates a four-way valve, a numeral 4 designates a outdoor heat exchanger, a numeral 5 designates a first expansion means to be used for heating operations, a numeral 6 designates a second expansion means to be used for cooling operations, numerals 7 and 8 respectively designate indoor heat exchangers, and a numeral 9 designates an accumulator. The above-mentioned devices are connected by refrigeration pipes in this order to form a refrigeration cycle.
A numeral 10 designates an oil level equalizing tube for connecting the shell of the first and second compressors 1, 2 at their lowest portions to equalize an amount of oil contained in the compressors. Numerals 11 and 12 designate check valves interposed between each outlet side of the compressors 1, 2 and the four-way valve 3, numerals 13 and 14 designate check valves each of which is connected in parallel to the expansion means 5 or 6, and numerals 15 and 16 designates solenoid valves each of which is provided at the inlet side of the indoor heat exchangers 7, 8 to be operated for the cooling operations.
In FIG. 6, solid arrow marks indicate the flow of a refrigerant when cooling and defrosting operations are carried out, and broken arrow marks indicate the flow of the refrigerant when the heating operations are carried out.
The operation of the conventional refrigeration cycle apparatus having the above-mentioned construction will be described.
In the cooling and defrosting operations, for instance, the refrigerant having a high temperature and a high pressure is discharged from the first and second compressors 1, 2; is passed through each of the check valves 11, 12, and is forwarded to the outdoor heat exchanger 4 by a switching operation of the four-way valve 3. The refrigerant becomes liquid by heat-exchanging in the heat exchanger 4. The liquid refrigerant is passed through the check valve 13 and is entered in the expansion means 6 where the pressure is reduced. The refrigerant having a low pressure is supplied to the indoor heat exchangers 7, 8 through the respective solenoid valves 15, 16 and the liquid refrigerant is again gasified by heat-exchanging. The refrigerant gas is returned to the first and second compressors 1, 2 through the four-way valve 3 and the accumulator 9. Thus, the refrigeration cycle for the cooling operation is obtainable by a single of the outdoor heat exchanger 4 and the indoor heat exchangers 7, 8 with the two compressors 1, 2. In the refrigeration cycle, the refrigerant is circulated while it is repeatedly subjected to liquefaction and evaporation.
In the heating operations, the refrigerant having a high temperature and a high pressure is discharged from the first and second compressors 1, 2 through their respective check valves 11, 12. The refrigerant is supplied to the indoor heat exchangers 7, 8 through the four-way valve 3. The refrigerant is liquefied by heat-exchanging in the heat exchangers 7, 8. The liquid refrigerant is then, passed through the solenoid valves 15, 16 and the check valve 14 to be forwarded into the expansion means 5 where the pressure of the liquid refrigerant is reduced. The refrigerant having a low pressure is again gasified by heat-exchanging in the outdoor heat exchanger 4. The gaseous refrigerant is again sucked into the first and second compressors 1, 2 through the four-way valve 3 and the accumulator 9. Thus, the refrigeration cycle for heating operations is attainable.
In the above-mentioned conventional refrigeration cycle apparatus, either or both of the compressors 1, 2 are selectively used depending on a load for the indoor heat exchanger during cooling or heating operations, and indoor heat exchangers 7, 8 are selected under the opening and closing control of the solenoid valves 15, 16. Namely, when one indoor heat exchanger 7 is selected, the solenoid valve 15 is opened and the solenoid valve 16 is closed. On the other hand, when the other indoor heat exchanger 8 is selected, the solenoid valve 16 is opened and the valve 15 is closed. When both of the heat exchangers 7, 8 are to be used, the solenoid valves 15 and 16 are opened.
The conventional refrigeration cycle apparatus did not have a container for storing a surplus amount of the refrigerant during its operation. Accordingly, when there was change in the load of the indoor heat exchanger, a suitable operation of the apparatus could not be obtained. For instance, when a load for cooling operation is large and both of the first and second compressors 1, 2 and both of the indoor heat exchangers 7, 8 are used, a large amount of refrigerant is required in the refrigeration cycle. On the other hand, when a load for heating operation is small wherein either of the compressors 1, 2 and either of the indoor heat exchangers 7, 8 are to be used, a small amount of the refrigerant is required. Thus, there is a great difference in an amount of the refrigerant between the load in the cooling operation and the load in the heating operation. When it is assumed that the heat-exchanging capacity of the indoor heat exchanger 7 is the same as that of the other heat exchanger 8, the optimum amount of the refrigerant required when the load for the heating operation is small, is about 30% as small as that the optimum amount of refrigerant required when the load for the cooling operation is large.
Accordingly, when an amount of the refrigerant filled in a refrigeration cycle apparatus is determined to obtain a suitable operational condition when the load for the heating operation is the minimum, there causes short of the refrigerant when the load for the cooling operation becomes the maximum, whereby the lifetime of the compressors 1, 2 is remarkably shortened because they are operated in an overheated state. On the other hand, when an amount of the refrigerant is determined to obtain a suitable operational condition when the cooling load is the maximum, the heating operation is carried out under the condition that the refrigerant is superfluous. This results in a liquid-back phenomenon in which some amount of liquid refrigerant is mixed in the gaseous refrigerant and is sucked into the compressors 1, 2 to thereby result in fault of the compressors.
Thus, in the conventional refrigeration cycle apparatus, it was difficult that a proper operational condition can be always obtained even though there was change of a load in the utilizable heat exchangers.
In the conventional apparatus, for instance, when an operation mode is changed from the heating operation to the defrosting or cooling operation, the liquid refrigerant condensed in the indoor heat exchangers 7, 8 flows in the accumulator 9 and the compressors 1, 2 through the four-way valve 3, whereby the compressors 1, 2 may be broken because a liquid compression is caused in the compressors. The same problem arises when an operation mode is changed from the defrosting or cooling operation to the heating operation. In order to eliminate such problem, it is necessary to use the accumulator 9 having a large capacity.
In the conventional refrigeration cycle apparatus, there has been found further problem as follows. For instance, when the cooling operation is stopped, the refrigerant is condensed and stays in the indoor heat exchangers 7, 8. On the other hand, when the heating operation is stopped, the refrigerant is condensed and stays in the outdoor heat exchanger 4. In either case, a large amount of the liquid refrigerant flows into the accumulator 9 when the compressors are started, and the liquid refrigerant further flows in the compressors 1, 2 in which the liquid compression is caused. The liquid compression may broke the compressors. To eliminate the problem, the capacity of the accumulator 9 should be made large.